This is a revised application proposing to continue a program of research to investigate sensory and perceptual processes in spoken communication. The primary aim of the research is to develop an empirical description and a theoretical account of the perceptual organization of speech. An allied aim of the research is to characterize the perceptual organization of multimodal speech perception, in which auditory and visual attributes are combined in a unified speech stream despite the dissimilarity of auditory and visual sensation. Although the motivation for this research is theoretical, it is specifically relevant to understanding the utility of the electrocochlear prosthesis despite the anomalous auditory qualities it evokes. Although many studies on the normal listener seek to explain the perceptual analysis of linguistic properties conveyed by speech, the present project is concerned with more fundamental functions by which the perceive finds and follows a single speech signal among concurrent sensory activity. This research aims to understand how the listener copes with apparently limitless variation in the superficial acoustic constituents of speech. In emphasizing the perceptual utility of abstract spectrotemporal properties, these studies may explain the robustness of speech perception with auditory qualities are altered or diminished by disease, and offers an opportunity to identify therapeutic accommodations for loss or failure of perceptual resources. Four projects comprising thirteen experiments are proposed for the coming five years. The research includes a set of studies with adult listeners to determine the contribution to the superficial acoustic form of speech signal elements to coarse grain phonetic perceptual organization; a detailed psychophysical evaluation of the interplay of auditory timbre and time-varying coherence in the perception of phonetic sequences composing words; a series of audiovisual tests of perceptual organization to analyze the phonetic effectiveness of spectrally and temporally manipulated acoustic components of speech in combination with a visual display of an articulating face; and, an appraisal of the perceptual reliance on time-varying acoustic structure that elicits the perception of the talker's identity as well as the spoken message. Together the investigations will elaborate fundamental processes of detecting and maintaining perceptual coherence, and will offer new evidence of the generality of a developing account of intermodal perception.